Every year Wizards of the Coast releases a product called the "Deckbuilder's Toolkit". It comes with 125 cards that are specifically chosen for this box as flexible, easy to understand cards that can be used to build your first Magic decks. It is a great product, comes with a storage box and a pamphlet of deckbuilding tips. This is a great gift for people that you want to get interested in the game.
Over the years I have taught a lot of folks to play Magic. It is a lot easier to teach with simple decks and I have always kept a couple specifically for teaching. That is where the toolbox came into being. I developed a custom box of magic cards with five 30 card mono-colored decks that could be combined in any combination to be used as a beginner's jumping off point for Magic. A lot of times if they were super enthusiastic I would let them keep it afterwards.
Funny thing though, I figured out my toolbox had other great uses. It made for a fantastic travel kit - The box is small enough for a purse or a bag and can be pulled out and played just about anywhere. Two people can pull a couple of colors and jump in - or even mix them all up and Winston or Winchester draft them as a mini-cube.
My toolbox that I keep for myself (not one I give away) is here if you would like to take a view. It is currently made up of cards from the Unlimited Edition of magic. It gives my toolkit a bit of a retro / nostalgia feel and makes it fun to tweak when I happen to find a cool, older card to upgrade my set. If you are making one to give away I would suggest building it from the current expansions. The look and feel and rules templating is much different, and you don't want to confuse them. New cards also give them cards that they can get excited about buying more of; and they can actually use them at FNM. I also try and avoid the more "fiddly" cards like things that generate tokens or require counters, as it is nice to keep the game footprint small in case you want to break it out in a pub or waiting in line at a convention.
If you are making one for travel, lunchtime or just for fun you can theme it however you want. Set it on a plane like Innistrad or Ravnica or just include mechanics that you really love. A lot of times this can even evolve into a small cube! In any case, a toolbox is a lot of fun to build and it can expose new people to a fantastic game!